The easiest method is isolation crossing. Assuming you have some blooming at the same time for both parents. You choose one as your seed parent and you have that in one pot surrounded by 4, 5, or 6 pots of the pollen parent. You might have a special plant you want to use as a pollen parent and you might have to divide the crown several times to get enough plants to effect this cross. But once you have this set of 6 pots, you can use them several times to cause crosses every few days for different seed parents. That is, you move the seed parents in and out of this area surrounded by the pollent parents. (Clear as green soup??) By sheer number of pollen, some large percentage of seed from the seed parent will be fertilized by the other plant. You need to keep all of the other flowering grasses some distance away. Once you have made the cross keep that plant (the seed parent) away from other pollen sources.

If I knew the species, we might be able to decide if all of this were necessary. Some of the grasses do not set self seed.